Lorenzo Bartolini

Pipe Strength and Deformation Capacity: A Novel FE Tool for the Numerical Lab

Future offshore pipelines development moves towards challenging operating condition and deep/ultra-deep water applications. Understanding the failure mechanisms and quantifying the strength and deformation capacity of pipelines, special components (buckle arrestors, wye, etc.) and in-line structures (in-line sled, in-line valve, in-line tee, etc.) is a need, under installation and operation loads, taking in account different geometrical characteristics and mechanical behaviors. The objective of this paper is to present and discuss recent FEM approaches integrating global and local analyses to evaluate the pipeline response and local effects, respectively. Thanks to this method the results coming from the global FEM analysis (main loads and driving phenomena) are used as input data for local FE Model with the aim to detect stress/strain intensification and other issues due to the local characteristics.In this paper:• The challenges of future deep water offshore pipelines are briefly presented;• The typical loading scenarios for pipelines during installation and operation are discussed;• The PipeONE 2014 tool, developed to facilitate the input/output data sharing between global and local FEM analyses, is presented and fully described in its main characteristics and capabilities;• An example is presented with the aim to understand and to appreciate the PipeONE 2014 functionality in FE modeling.© 2014 ASME

A Numerical Lab to Predict the Strength Capacity of Offshore Pipelines

In the recent years, the offshore pipeline industry has been under pressure to provide solutions for demanding material and line pipe technology problems, installation technology to safely tackle the ultra-deep waters challenge, quantitative prediction of reliable operating lifetime for pipelines under high pressure/high temperature conditions and remedial measures to tackle considerable geo-morphic and human activity related hazards. Future pipelines are being planned in very difficult environments, i.e. crossing ultra-deep water and difficult geo-seismic-morphic conditions. In these circumstances, it is of crucial importance (1) to adopt advanced design procedure and criteria, possibly based on limit state principles recently implemented in the design codes, and (2) to use advanced engineering tools for predicting the strength capacity and the pipeline behaviour during the installation and operational phase, in order to design the pipeline safely and to assess properly the technic-economical feasibility of the project. This paper discusses the relevant failure modes for offshore pipelines, the FE analysis results relevant to the sectional capacity of thick-walled pipes, and the FE analysis results relevant to the global and local response effect of a pipeline, laid on the sea bottom, and subject to a point-load force.Copyright

HotPipe JI Project: Experimental Test and FE Analyses

In the last twenty years, experimental tests and FEM-based theoretical studies have been carried out to investigate the buckling mechanisms of thin-walled pipes subject to internal pressure, axial force and bending moment. Unfortunately, these studies do not completely cover the scope relevant for offshore pipelines i.e. outer diameter to thickness ratio lower than 50. In the HotPipe Phase 2 JI Project, full-scale bending tests were performed on pressurized pipes to verify the Finite Element Model predictions from HotPipe Phase 1 of the beneficial effect of internal pressure on the capacity of pipes to undergo large plastic bending deformations without developing local buckling. A total of 4 pipes were tested, the key test parameters being the outer-diameter-to-wall-thickness ratio (seameless pipes with D/t = 25.6, and welded UOE pipes with D/t = 34.2), and the presence of a girth weld in the test section. For comparison a Finite Element Model was developed with shell elements in ABAQUS. The test conditions were matched as closely as possible: this includes the test configuration, the stress-strain curves (i.e. using measured curves as input), and the loading history. The FE results very realistically reproduce the observed failure mechanisms by formation and localization of wrinkles on the compression side of the pipe. Good agreement is also achieved in the moment capacities (with predictions only 2.5 to 8% above measured values), but larger differences arose for the deformation capacity, suggesting that the DNV OS-F101 formulation for the characteristic bending strain (which is based on FE predictions from HotPipe Phase I) may be non-conservative in certain cases.Copyright

In-Service Buckling Assessment: The Correct Use of Engineering Analysis Tools

There is consensus on the need for in-service buckling analyses to assess the integrity of both flowlines and long distance trunklines subject to HP/HT service condition. The extent of the analyses and supporting survey depends on the severity of the application.In the last two decades, the pipeline industry has gained significant experience in both the design and operation of pipeline systems exposed to global buckling. Actually, the early 90s have been a watershed: before the phenomenon was just known (theoretically), then it was seen...as soon as pipeline integrity management programmes have been introduced in the offshore pipeline industry practices. Although, limited information have been documented in the open literature, now as then.Several efforts have been dedicated to develop design methods and procedures suitable for operating pipeline safely as well as protecting the population, environmental resources and assets. At the beginning, there was a gap to be closed as specific mitigation measures were never designed. Nowadays, thanks to computational progress, it seems that the attention is addressed to face the uncertainties affecting the subject matter but, sometime, leading to overdesign.The scope of the paper is to present aspects of global buckling design analyses that were performed in recent projects with the aim to highlight the challenges and the risks, the accuracy or the limitation of the methods, the feedback and the lesson learnt of real installed pipelines under operating conditions.Copyright

VIV Basics for Subsea Spool/Jumper Design

Coming and future Deep and Ultra-Deep Water project developments involve the use of many Subsea Rigid Jumpers used to connect well heads, manifolds or riser base with Flowline End Terminations.Generally, Subsea Rigid Jumpers are short and flexible pipe sections assembled in a variety of spatial configurations to accommodate the installation tolerances, the Flowline End Terminations translation and settlement guaranteeing the continuity and the flexibility needs of the subsea pipe layout. These Subsea Rigid Jumpers are critical components as they are subject to fatigue damage due to Vortex Induced Vibrations induced by the bottom currents and/or Flow Induced Vibrations induced by the high internal flow rate, often coupled with slugging flow conditions.In this paper, a Subsea Rigid Jumper design approach based on basics of Vortex Induced Vibrations is presented, and outcomes on a few typical multi-planar Subsea Rigid Jumpers discussed.Copyright

Strain Based Design: Crossing of Local Features in Arctic Environment

In arctic pipeline projects, seismic risk and differential settlements are common, whether local or distributed across long stretches. For buried pipelines, seismic hazards are generally classified as wave propagation hazard (WP) or permanent ground deformation (PGD) hazard. Below ground crossing of seismic faults has been the real challenge in a series of pipeline projects. STress Based Design (STBD) criteria has been used in the past. Application of this method is straightforward as simple linear elastic analysis is required to calculate the load effects in the specified conditions. In the assessment of the structural integrity of a pipeline, load effects are compared with allowable states of stress. Unfortunately, unsatisfactory design, both from economic and safety points of view, may result. StraiN Based Design (SNBD) is an attractive option in these situations.The use of SNBD in pipeline technology has been widely discussed during the last decade, particularly for offshore applications. In many instances the offshore pipeline engineer can adopt SNBD to avoid onerous measures necessary to meet the traditional STBD criteria. First introduced to make allowance for crossing bottom roughness and harsh environments, more recently for High Pressure/High Temperature (HP/HT) applications, SNBD is currently used in a series of strategic project developments in North America and East Siberia, for both offshore and land pipelines crossing regions affected by ice gouging and geo-hazards from seismic activity such as land slides, active faults, soil lateral spreading due to soil liquefaction etc. Conditions for which SNBD are applicable, as well as permissible deformations in relation to line pipe material and safe operation of the pipeline in the long run, are of major concern.In this paper, the following is discussed:• Relevant hazards for arctic land and offshore pipelines such as ice scouring, permafrost thaw, frost heave etc..• The design approach and design philosophy for Buried Pipeline Crossing active faults. In particular:○ The Pipeline Crossing Layout of local features to minimize Load Effects;○ Material and Steel Wall Thickness Selection vs. Crossing Location;○ Pipeline Deformation Capacity (PDC) Assessment;○ Pipeline Strain Demand (PSD) Assessment;○ Pipeline Trench Design including Shape, Back-filling etc. vs. Pipe-Soil and Temperature Effects.Copyright

Deformation Capacity of Induction Bends

In the last two decades, reliability methods have been extensively used to calibrate rationally-based Load and Resistance Factored Design (LRFD) equations for the design of offshore and onshore pipelines. Several experimental and theoretical studies have been carried out with the aim to assess the strength and deformation capacity of induction bends, when buried and subject to severe and extreme loading conditions such as the ones caused by an earthquake crisis. Design criteria for induction bends do not reflect the R & D efforts of the recent years and working stress design in generally accepted by the Industry. The scope of this paper is: • Review the relevant literature on bends discussing analytical solutions, numerical analyses and experimental tests carried out aiming to predict the limit loads/deformations of induction bends and to define design criteria for induction bends. • Discuss the ABAQUS Finite Element Model (FEM) developed; • Present the FEM development, calibration and validation; • Show the parametric study results considering relevant parameters including bend geometry (wall thickness and bend angle), fabrication tolerances (thickness variation, bend cross section etc.), steel material characteristics (hardening and shape), and loading conditions (inner pressure, steel axial force, bending moment under closing and opening mode).Copyright

Effects of Underwater Explosion on Pipeline Integrity

Unexploded charges e.g. mines, bombs, torpedoes, etc... are rarely identified at a very early stage of reconnaissance surveys for pipeline route corridors. These ordnances are found during detailed pre-engineering or pre-lay surveys and, sometimes and not surprisingly, during the ordinary surveys performed on the pipeline in service. UXOs represent a hazard for the pipeline as well as for the assets and people involved in the construction phase. An appropriate mitigation plan in areas potentially affected is generally performed, including ordnance removal or mined-area clearance. Large diameter long offshore trunk lines crossing different territorial waters are often exposed to this kind of hazard. As such, pipeline construction and operation call for advanced numerical modelling as unique/valuable tool for providing a quantitative measure of the UXOs related risks.In recent projects the understanding of the underwater explosion process and prediction of damages associated to specific weapon-target engagement are based on the outcome of engineering tools based on finite element modelling. The continuing development of multi-purpose and multi-physics finite element analyses codes facilitates their application, providing sharp and detailed insight into the complex subject of underwater explosive effect and the coupled response of nearby structures. The scope of the structural integrity assessment is to define the minimum distance to be guaranteed between the pipeline and unexploded ordnance to avoid any risk of pipeline damage, as a function of the quantity of explosive. The engineering task of the integrity assessment includes the definition of the relevant conditions for the pipeline whether buried or free spanning, the analysis of the interaction between the gas bubble and shock pressure waves and the cylindrical shape of the pipeline, both as a shell that collapse under a pressure wave and a pipe length that moves laterally and develops bending. The objective is to evaluate the minimum allowable distance of the ordnance from the pipeline, as a function of the explosive quantity and type.In this paper, a series of real cases is presented in order to provide the most relevant parameters characterizing the integrity assessment under the applied load scenario from propagating shock waves. The propagation in water of shock pressure waves induced by the underwater explosion of a spherical charge is performed using finite element modelling, after model verification and validation with respect to the analytical and experimental formulations available in open literature. The outcome from finite element modelling is compared with findings from a simplified model based on modal analysis of the pipe shell – inward bulging and collapse of the pipe section and of the pipe beam – lateral displacement of the impacted stretch and bending at the crest of the buckle.Copyright

Advanced Analysis and Design Tools for Offshore Pipeline in Operation

In the last thirty years, the attention of the offshore pipeline industry has been strongly focused on submarine pipelines crossing very uneven seabed. New pipelines crossing the uneven seabed of the Mediterranean Sea and of the North Sea and deep water pipelines crossing the uneven continental slope of the Gulf of Mexico are outstanding examples. Pipeline structural integrity may be threaten by large free-spanning sections between rocky peaks and deep depressions that may be coupled with the pipeline propensity to develop lateral/vertical deflection due to severe service conditions (High Pressure/High Temperature). Generally, these scenarios require mitigation measures aiming to control the development of excessive bending moment/deformation by means of Finite Element (FE) Modeling. FE Modeling gives a valuable contribution to the pipeline engineering at identifying a technical and cost effective solution since the early phase of the project. Finite Element (FE) Model approaches, based on standard structural finite element codes available on the market, such as ABAQUS, ADINA, ANSYS etc., are commonly used to analyze the effects of non-linearity, e.g. steel material, soil-pipe interaction and large rotations/displacements. 3-Dimensional FE Models permit to predict the overall pipeline global response under design loads taking into account the expected (during design phase) and/or actual (after measurements gathered during as-built survey campaign) 3-Dimensional pipeline configuration including 3-Dimensional (along and transversal to the pipeline route) bottom roughness, route bends, intervention works for bottom roughness and free-span correction and mitigation measures against HP/HT condition in operation. In this paper: • The design approach for HP/HT pipelines is described; • The main features of the ABAQUS FE Model, developed to predict the behavior of offshore pipelines in operation, are presented; • Two relevant examples of offshore pipelines subject to pressure and temperature conditions are presented with and without mitigation measures.Copyright